The present invention relates to an apparatus and a method for conveying in a relatively short distance curved glass sheets having two-dimensional simple curvature or three-dimensional compound curvature.
There are several methods for bending glass sheets such as automotive window glass. In one method, a glass sheet is heated to become soft and bent by making the heated glass sheet sag by gravitation in a mold. In another method, a glass sheet is heated and then pressed by press molds. In still another method, a glass sheet is heated and bent while floatingly conveyed over hearth beds in a furnace. More specifically, while the glass sheet is conveyed over a series of hearth beds in a conveyance direction, hot gas is ejected toward the glass sheet so that the glass sheet is floated over the hearth beds. The hearth beds have upper surfaces curved along a plane perpendicular to the conveyance direction. The glass sheet is thus heated with the hot gas, gradually sags by gravitation and is bent according to the curvature of the upper surfaces of the hearth beds. In a subsequent stage, the bent glass sheet is quenched in a quenching unit. Alternatively, the glass sheet may be conveyed by a series of rolls in the furnace and bent according to the curvature of the rolls. This method may be referred to as “hearth roll bending method”. A decision as to which method should be used is made depending on the size and curvature of bent glass sheets to be fabricated.
In the method using the hearth beds in the furnace (hereinafter referred to as a hearth bed bending method), it is necessary to fabricate in the same furnace glass sheets of a simple curvature, which are bent in a direction perpendicular to the conveyance direction, and glass sheets of a compound curvature, which also have a curvature in the conveyance direction. In order to maintain high productivity of the hearth bed bending method, it is desirable to have a production procedure that is capable of achieving a fast production procedure change upon switching the type of the glass sheets.
There are known several apparatuses for conveying glass sheets of a compound curvature (see U.S. Pat. No. 3,409,422 corresponding to Japanese Patent Examined Publication 49-10331; U.S. Pat. No. 4,540,426 corresponding to Japanese Patent Unexamined Publication 60-86042; and U.S. Pat. No. 6,014,873 corresponding to Japanese Patent Unexamined Publication 5-9037). It is described in these publications that glass sheets are bent into a compound curvature while they are continuously conveyed and that after cooling the glass sheets of a compound curvature are conveyed by an apparatus to a subsequent step.
It is disclosed in U.S. Pat. No. 3,409,422 that the level, at which glass sheets of a compound curvature are transferred to a conveyor roll, becomes inevitably low, since glass sheets are downwardly conveyed while they pass over the hearth beds and through the quenching unit. Thus, a lift-up apparatus should be used for making the level of the glass sheets higher as long as a conventional production line of a hearth bed bending method is used. This publication, however, does not have a specific description of a conveying mechanism for transferring glass sheets of a compound curvature from a low level position to a high level position after the quenching unit.
U.S. Pat. No. 4,540,426 discloses an apparatus for upwardly conveying glass sheets. During conveyance, the glass sheets are held between support rolls and holding rolls. This apparatus is necessarily provided with a disposition of two opposing rows of conveyor rolls and with a mechanism for adjusting and maintaining the distance between each two opposing rolls.
U.S. Pat. No. 6,014,873 discloses an apparatus for conveying glass sheets of a compound curvature. In this apparatus, a disc roll conveyor is connected at a position downstream of a quenching device in a manner to incline downwardly and tilt toward one side. As glass sheets of a compound curvature are conveyed on the disk roll conveyor, their position is changed from the tilted position to a horizontal position. Then, the glass sheets are transferred to an upwardly inclined belt conveyor and then to a post-treating horizontal belt conveyor. It is, however, difficult to smoothly convey curved glass sheets by this apparatus, when the level of the outlet of the quenching device is considerably different from that of the upstream end of the post-treating horizontal belt conveyor. To prevent this difficulty, the upward slope of hearth beds is made steeper in this publication.
There are two proposals relating to hearth beds in a furnace for shortening the time required to change the conveyance of glass sheets having a simple curvature to that of glass sheets having a compound curvature and vice versa (see U.S. Patent Application Publication No. 2002/0148254 A1 corresponding to Japanese Patent Unexamined Publication 2002-316828; and U.S. Patent Application Publication No. 2003/0110801 A1 corresponding to Japanese Patent Unexamined Publication 2003-226532).